Phase 5-7: README, Makefile, unit tests

- README.md: full usage docs
- Makefile: build/install/uninstall/test/lint/clean targets
- config/config_test.go: 7 tests (load, save, find, add, roundtrip, invalid yaml)
- runtime/runtime_test.go: 6 tests (get, available, ListRunning graceful degradation)
- systemd/generator_test.go: 7 tests (ServiceName, Generate system/user/custom/docker/unknown, buildExecCommands)
- fix: docker/podman ListRunning returns nil (not error) when daemon unavailable
- fix: invalid YAML test uses tab-indent which is genuinely unparseable

config/config_test.go

@@ -0,0 +1,146 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadOrEmpty_NoFile(t *testing.T) {
+	cfg, err := LoadOrEmpty("/tmp/unitdore-nonexistent-test.yaml")
+	if err != nil {
+		t.Fatalf("expected no error for missing file, got: %v", err)
+	}
+	if len(cfg.Units) != 0 {
+		t.Errorf("expected empty units, got %d", len(cfg.Units))
+	}
+}
+
+func TestSaveAndLoad(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "units.yaml")
+
+	cfg := &Config{
+		Units: []Unit{
+			{Name: "nginx", Runtime: "podman", Order: 1, Enabled: true},
+			{Name: "myapp", Runtime: "docker", User: "hein", Order: 2, Enabled: true},
+		},
+	}
+
+	if err := cfg.Save(path); err != nil {
+		t.Fatalf("Save failed: %v", err)
+	}
+
+	loaded, err := Load(path)
+	if err != nil {
+		t.Fatalf("Load failed: %v", err)
+	}
+
+	if len(loaded.Units) != 2 {
+		t.Errorf("expected 2 units, got %d", len(loaded.Units))
+	}
+	if loaded.Units[0].Name != "nginx" {
+		t.Errorf("expected nginx, got %s", loaded.Units[0].Name)
+	}
+	if loaded.Units[1].User != "hein" {
+		t.Errorf("expected user hein, got %s", loaded.Units[1].User)
+	}
+}
+
+func TestFindUnit(t *testing.T) {
+	cfg := &Config{
+		Units: []Unit{
+			{Name: "nginx", Runtime: "podman"},
+			{Name: "myapp", Runtime: "docker"},
+		},
+	}
+
+	u := cfg.FindUnit("nginx")
+	if u == nil {
+		t.Fatal("expected to find nginx, got nil")
+	}
+	if u.Runtime != "podman" {
+		t.Errorf("expected podman, got %s", u.Runtime)
+	}
+
+	missing := cfg.FindUnit("nothere")
+	if missing != nil {
+		t.Errorf("expected nil for missing unit, got %+v", missing)
+	}
+}
+
+func TestAddUnit(t *testing.T) {
+	cfg := &Config{}
+
+	added := cfg.AddUnit(Unit{Name: "nginx", Runtime: "podman", Enabled: true})
+	if !added {
+		t.Error("expected AddUnit to return true for new unit")
+	}
+	if len(cfg.Units) != 1 {
+		t.Errorf("expected 1 unit, got %d", len(cfg.Units))
+	}
+
+	// Adding a duplicate should return false and not grow the list
+	added = cfg.AddUnit(Unit{Name: "nginx", Runtime: "docker"})
+	if added {
+		t.Error("expected AddUnit to return false for duplicate")
+	}
+	if len(cfg.Units) != 1 {
+		t.Errorf("expected still 1 unit, got %d", len(cfg.Units))
+	}
+}
+
+func TestLoad_InvalidYAML(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "bad.yaml")
+	// Use a tab character in a mapping key — this is genuinely invalid YAML
+	os.WriteFile(path, []byte("units:\n  - name: ok\n\t  broken: tab-indent"), 0644)
+
+	_, err := Load(path)
+	if err == nil {
+		t.Error("expected error for invalid YAML, got nil")
+	}
+}
+
+func TestSave_CreatesParentDir(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "subdir", "nested", "units.yaml")
+
+	cfg := &Config{Units: []Unit{{Name: "test", Runtime: "podman", Enabled: true}}}
+	if err := cfg.Save(path); err != nil {
+		t.Fatalf("Save failed to create parent dirs: %v", err)
+	}
+
+	if _, err := os.Stat(path); err != nil {
+		t.Errorf("expected file to exist: %v", err)
+	}
+}
+
+func TestDisabledReason_Roundtrip(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "units.yaml")
+
+	cfg := &Config{
+		Units: []Unit{
+			{
+				Name:           "ghost",
+				Runtime:        "podman",
+				Enabled:        false,
+				DisabledReason: "container not found",
+			},
+		},
+	}
+
+	if err := cfg.Save(path); err != nil {
+		t.Fatalf("Save failed: %v", err)
+	}
+
+	loaded, err := Load(path)
+	if err != nil {
+		t.Fatalf("Load failed: %v", err)
+	}
+
+	if loaded.Units[0].DisabledReason != "container not found" {
+		t.Errorf("expected disabled_reason to survive roundtrip, got: %q", loaded.Units[0].DisabledReason)
+	}
+}